546 



Philip Lake — Direction of Faults. 



they will lie between the outcrops on the upthrow side (Fig. 3). 

 A little cx)nsideration will make it clear that the position of the 

 anticlinal axis upon the map is entirely unaifected by such a fault, 

 because it has simply been shifted vertically. If, however, the 

 movement of the one face of the fault upon the other has been 

 horizontal instead of vertical, the whole anticlinal will have been 

 thrown to one side ; and the outcrops on one side of the fault will 

 no longer, if produced, lie between the outcrops on the other side 

 (Fig. 4).^ 



7r\ 



3 



3 



Fi^. 



J. 



Fzcf- 4 



Anticlinal faulted by a fault, the 

 movement along which has been 

 vertical. 



Anticlinal faulted by a fault, the 

 movement along which has been 

 horizontal. 



A shows the two faces of the fault, as in Figs. 1 and 2. B Plan. 



Cases of this kind are by no means rare, and must have led many 

 geologists to reflect that no amount of vertical movement can account 

 for them. Between Aber and Bethesda, for example, there is an 

 anticlinal of Lingula Grits crossed by a series of parallel faults. 

 Most of the faults produce no effect upon the axis of the anticlinal, 

 but the one on Ffridd-du shifts the whole anticlinal several hundreds 

 of yards to one side.^ More striking still is the fact that during one 

 or two recent earthquakes visible faults have been formed accom- 

 panied by a lateral displacement of the ground on one side of 

 the fault.' 



^ The converse case of a synclinal is so similar that it is unnecessary to refer to 

 it here. 



^ See Quarter -sheet 78 S.E. of the Geological Survey of England and "Wales. 

 A map of the area is also given in " The Geology of North "Wales" (Mem. Geol. 

 Surv., vol. iii), 2ud ed., p. 202. 



3 See, for example, " JSTotes on the Earthquake in Baluchistan on the 20th 

 December, 1892," by C. L. Griesbach : Rec. Geol. Surv. India, vol. xxvi (1893), 

 pp. 57-61, 3 plates. The chief evidence of lateral displacement is the disturbance of 



